Loudspeaker having a composite diaphragm structure

ABSTRACT

A shallow loudspeaker provided with a chassis ( 2 ), a movable body ( 4 ), a resilient suspension for guiding the movable body with respect to the chassis along a translation axis (T), and an electric actuator ( 6 ) for driving the movable body along the translation axis. The movable body has a diaphragm structure comprising a central domeshaped diaphragm ( 8 ) and a cone-shaped diaphragm ( 10 ) concentrically arranged with respect to the dome-shaped diaphragm. The cone-shaped diaphragm has a back portion ( 10   b ) and a front portion ( 10   f ) which is wider than the back portion. Both diaphragms are attached to each other near the back portion of the cone-shaped diaphragm, the cone-shaped diaphragm enveloping the dome-shaped diaphragm. The resilient suspension comprises a first resilient element ( 12   a ) connecting the diaphragm structure to the chassis near the back portion of the cone-shaped diaphragm, and a second resilient element ( 12   b ) connecting the diaphragm structure to the chassis near the front portion of the cone-shaped diaphragm.

The invention relates to a loudspeaker provided with a chassis, amovable body, a resilient suspension for guiding the movable body withrespect to the chassis along a translation axis, and an electricactuator for driving the movable body along the translation axis.

Speakers of such a type are generally known; e.g. PCT Patent ApplicationWO 96/14722 discloses such a loudspeaker. This known loudspeaker has aframe, a membrane and an electromagnetic driving unit. The membrane isformed by a conical body and has an outer circumferential edge and aninner circumferential edge. The driving unit is provided with astationary part and a movable part. The stationary part includes apermanent magnet and a magnetic yoke and is secured to the frame. Themovable part includes a voice coil and a cylindrical coil support. Atits outer circumferential edge, the membrane is connected to the frameby means of a flexible suspension and, at its inner circumferentialedge, it is adhered to the coil support, which in its turn is connectedto the frame by means of a spider.

The conical membrane of the known loudspeaker has a certain height inorder to obtain sufficient stiffness. The membrane must have a certainminimal stiffness in order to be able to move like a piston, not onlyfor low frequency reproduction but for the whole or at least the largerpart of the audio spectrum.

For this reason, there arise problems relating to the speaker'sperformance when a shallow speaker, i.e. a speaker having a smallheight, is required in certain applications.

It is an object of the invention to improve the known loudspeaker insuch a way that it can be given a small height without degrading itssound performance.

This object is achieved with the loudspeaker according to the invention,which is provided with a chassis, a movable body, a resilient suspensionfor guiding the movable body with respect to the chassis along atranslation axis, and an electric actuator for driving the movable bodyalong the translation axis, which movable body has a diaphragm structurecomprising a centrally situated dome-shaped diaphragm and adecentralized cone-shaped diaphragm concentrically arranged with respectto the dome-shaped diaphragm, which cone-shaped diaphragm has a backportion and a front portion which is wider than the back portion,wherein both diaphragms are attached to each other near the back portionof the cone-shaped diaphragm, the cone-shaped diaphragm enveloping thedome-shaped diaphragm, and wherein the resilient suspension comprises aresilient element connecting the diaphragm structure to the chassis nearthe back portion of the cone-shaped diaphragm, and a further resilientelement connecting the diaphragm structure to the chassis near the frontportion of the cone-shaped diaphragm.

Thus, the loudspeaker according to the invention has a diaphragmstructure which is composed of an outwardly convex, particularlydome-shaped, diaphragm and a cone-shaped diaphragm situated around theother diaphragm. This makes it possible to give the diaphragm structureof the movable body sufficient stiffness to prevent an undesiredbreak-up, i.e. bending wave resonances, during mid and high-frequencyreproduction in relatively flat loudspeaker constructions. In principle,a cone-shaped diaphragm known per se may be used. The same applies tothe dome-shaped diaphragm. A rigid dome-shaped diaphragm known per semay be used. Such diaphragms are known, for instance, from U.S. Pat. No.3,925,626. The loudspeaker according to the invention can be driven by ausual audio transformer of an amplifier system known per se.

A favorable embodiment of the loudspeaker according to the invention hasthe characteristic feature that the electric actuator comprises astationary part which is secured to the chassis or to a stationaryelement fixed to the chassis and further comprises a translatable partwhich is secured to the dome-shaped diaphragm. Due to this feature, thetranslatable part of the electric actuator extends into the spaceenveloped by the dome-shaped diaphragm.

It is to be noted that said U.S. Pat. No. 3,925,626 discloses anall-frequency loudspeaker which has a domed diaphragm instead of theusual cone diaphragm of the prior art in order to get, inter alia, ahigh-fidelity sound. Secured to the underside of the diaphragm is a formwhich extends downwards into an air gap formed by a pole piece and atopring of a magnet system and on which a voice coil has been wound. Thedevice formed by the diaphragm and the form is suspended from aframework by means of a resilient suspension secured to both thediaphragm and the framework and a resilient support secured to both theform and the framework. A disadvantage of this known loudspeaker is itsheight, which has to be substantial in order to provide sufficientdistance between the lower resilient support and the topring to realizethe required travel of the diaphragm. Contrary to the known devices, theloudspeaker according to the invention has no suspension means securedto the coil support, and thus does not have the above-describeddisadvantage.

In a practical embodiment of the loudspeaker according to the invention,the back portion of the cone-shaped diaphragm includes an innercircumferential edge to which an outer circumferential rim of thedome-shaped diaphragm is connected, said edge and rim being preferablyattached to each other by means of an adhesive, such as a glue. In thiscontext it is also preferred to connect an inner circumferential brim ofthe resilient element of the resilient suspension to the innercircumferential edge of the cone-shaped diaphragm and/or to the outercircumferential rim of the dome-shaped diaphragm. This can also berealized by means of a suitable adhesive.

In another practical embodiment, the stationary part includes a magneticyoke with a permanent magnet and the translatable part includes a coilsupport with a voice coil, which coil extends in an air gap of themagnetic yoke and has a coil axis coinciding with the translation axisof the movable body.

It is to be noted that the loudspeaker according to the invention issuitable for sound reproduction in hifi, home, automotive, TV andmultimedia systems and, as already indicated, is particularly suitablefor applications having very small built-in depths.

The invention also relates to a diaphragm structure intended for use inthe loudspeaker according to the invention. Particularly, the diaphragmstructure according to the invention has the characterizing feature thatit is composed of a central dome-shaped diaphragm and a cone-shapeddiaphragm concentrically arranged with respect to the dome-shapeddiaphragm. For a further description, reference is made to claim 6.

The invention further relates to a loudspeaker unit comprising theloudspeaker according to the invention and also comprising a housingaccommodating the loudspeaker.

It is noted in relation to the claims that various combinations ofcharacteristic features defined in the claims are possible.

The above-mentioned and other aspects of the invention are apparent fromand will be elucidated, by way of non-limitative examples, withreference to the embodiment described hereinafter.

In the drawings:

FIG. 1 shows an embodiment of the loudspeaker according to the inventionin a diagrammic cross-section, and

FIG. 2 is a perspective elerational view of the loudspeaker of FIG. 1 inan exploded view.

The electrodynamic loudspeaker according to the invention, shown in theFigures, comprises a chassis 2, a movable body 4 and an electromagneticactuator 6. For forming a loudspeaker unit according to the invention,the loudspeaker may be accommodated in a housing. To this end, thechassis 2 may be fixed in an appropriate opening in a wall of thishousing. In FIG. 1, the housing is shown diagrammatically by means of awall section 1 in broken lines.

The movable body 4 has a three-dimensional diaphragm structurecomprising a central dome-shaped diaphragm 8 and a cone-shaped diaphragm10 concentrically arranged with respect to the dome-shaped diaphragm 8.The dome-shaped diaphragm 8 may be made of a metal, such as aluminium;reinforced plastics; pressed paper; or any other suitable material. Thediaphragm 8 has a sufficient stiffness and may be provided with acentral opening 8 a covered by a dust cap 9 of any suitable material,such as paper, plastics, or textile. The cone-shaped diaphragm 10 may bemade of pressed paper, carbon fiber, polyglass, aluminium, or any othersuitable material. The cone-shaped diaphragm 10 has a back portion 10_(b) and a front portion 10 _(f) which is wider than the back portion 10_(b). The dome-shaped diaphragm 8 and the cone-shaped diaphragm 10 aremutually secured at the back portion 10 _(b). For this reason, thecone-shaped diaphragm 10 has an inner circumferential edge 10 _(i),while the dome-shaped diaphragm 8 has a corresponding outercircumferential rim 8 _(o). The edge 10 i and the rim 8 _(o) preferablyhave round cross-sections so that the edge 10 _(i) and the rim 8 _(o)fit each other. The edge 10 _(i) and the rim 8 _(o) are preferably gluedto each other.

The loudspeaker further comprises a resilient suspension for suspendingthe movable body 4 from the chassis 2 and for guiding the movable bodyalong a translation axis T. The suspension includes a first resilientelement 12 a and a second resilient element 12 b. The first resilientelement 12 a is a ring-like spider, an inner circumferential brim 12 a_(i) of which is attached to the edge 10 _(i) and/or the rim 8 _(o) andan outer circumferential brim 12 a _(o) is attached to the chassis 2. Aglue may be used for both attachments. The spider 12 a may be a knownflexible corrugated body and ensures that the movable body 4 can performwell-defined translation movements with respect to the chassis 2.

The second resilient element 12 b has a roll structure known per se andis formed, for example, from a bent rubber or foam annular strip. On itsouter circumference, the second element 12 b is secured, for exampleglued, to the chassis 2 and on its inner circumference to an outercircumferential edge 10 _(o) of the cone-shaped membrane 10.

The actuator 6 essentially comprises two elements, namely a stationaryactuator part 6 a which is fixed to the chassis 2 and a translatableactuator part 6 b which is connected to the movable body 4 . One of theactuator parts—in this example the part 6 a—is provided with a permanentmagnet 13, in this example annular in shape and axially polarized, andthe other actuator part—in this example the part 6 b—is provided with amagnet coil 14. The permanent magnet 13 is formed from aneodymium-iron-boron alloy and forms a magnetic yoke 13 a with soft ironportions of the stationary actuator part 6 a, which yoke defines an airgap 16. The magnet coil 14, being a cylindrical coil, also referred toas voice coil, is situated on a coil support 14 a, being a sleeve inthis example, which is fixed to the dome-shaped diagram 8. A lead wire17 connects the coil 14 by means of a connector 18 which is adhered tothe chassis 2. When energizing the coil 14, both actuator parts 6 a, 6 bmagnetically co-operate with each other over the air gap 16 forgenerating a driving force on the movable body 4 parallel to thetranslation axis T and thus on the dome-shaped diaphragm 8 and thecone-shaped diaphragm 10.

It is to be noted that the invention is not limited to the embodimentshown. For example, the dome-shaped diaphragm and the cone-shapeddiaphragm may be formed as an integral combination, thus comprising orconsisting of a single diaphragm structure. Moreover, the loudspeakerunit may not only comprise one or more speakers but also one or morepassive radiators or bass reflex ports. Furthermore, the loudspeakeraccording to the invention is not limited to a certain power. Foracoustical sound tuning purposes, the dome-shaped diaphragm may beprovided with perforations and/or a coating. For the same purposes, theouter circumferential rim of the dome-shaped diaphragm does not need tobe a back portion of the dome-shaped diaphragm, but may be a rimparallel to the back portion.

1. A loudspeaker provided with a chassis, a movable body, a resilientsuspension for guiding the movable body with respect to the chassisalong a translation axis, and an electric actuator for driving themovable body along the translation axis, which movable body has adiaphragm structure comprising a central dome-shaped diaphragm and acone-shaped diaphragm concentrically arranged with respect to thedome-shaped diaphragm, which cone-shaped diaphragm has a back portionand a front portion which is wider than the back portion, wherein bothdiaphragms are attached to each other near the back portion of thecone-shaped diaphragm, the cone-shaped diaphragm enveloping thedome-shaped diaphragm, and wherein the resilient suspension comprises aresilient element connecting the diaphragm structure to the chassis nearthe back portion of the cone-shaped diaphragm, and a further resilientelement connecting the diaphragm structure to the chassis near the frontportion of the cone-shaped diaphragm.
 2. A loudspeaker as claimed inclaim 1, wherein the electric actuator comprises a stationary partsecured to the chassis and a translatable part secured to thedome-shaped diaphragm.
 3. A loudspeaker as claimed in claim 1, whereinthe back portion of the cone-shaped diaphragm includes an innercircumferential edge to which an outer circumferential rim of thedome-shaped diaphragm is connected.
 4. A loudspeaker as claimed in claim3, wherein the resilient element of the resilient suspension includes aninner circumferential brim which is connected to the innercircumferential edge of the cone-shaped diaphragm and/or the outercircumferential rim of the dome-shaped diaphragm.
 5. A loudspeaker asclaimed in claim 2, wherein the stationary part includes a magnetic yokewith a permanent magnet and the translatable part includes a coilsupport with a voice coil, which coil extends in an air gap of themagnetic yoke and has a coil axis coinciding with the translation axisof the movable body.
 6. A diaphragm structure presenting the features ofthe diaphragm structure disclosed in claim 1 and thus constructed andevidently intended for use in the loudspeaker as claimed in any one ofthe preceding claims.
 7. A loudspeaker unit comprising the loudspeakeras claimed in claim 1 and comprising a housing accommodating theloudspeaker.